Strongly foul-smelling biological waste gases are produced, for example, in animal utilizing plants, fish meal factories, large cattle sheds and where cattle are kept in large numbers. To deodorize waste gas it is known that foul-smelling constituents in the waste gases are often decomposable by being washed with aqueous acid formed by dissolving an acid-forming gas in water. This is particularly true when the waste gas is a biological waste gas as described above. Chlorine and sulphur dioxide are often used as the acid-forming gases, although others can be used.
The normal way of carrying out the process is to mix the waste gases and acid-forming gases with a flowing stream of water in a layer of moist limestone. The desired reaction takes place at the surfaces of the pieces of limestone, the gas mixture passes through the layer of limestone while the salts formed are washed off the limestone by the flowing stream of water.
The process is effective in that biological and other waste gases leaving the limestone layer are practically odorless and ready for discharge into the atmosphere and the materials used in the process are relatively cheap. However, in order to achieve this adequate deodorization, the bed of limestone has to be such that there is considerable pressure loss across it, as a result of which it is necessary to provide powerful, and therefore expensive, pumping apparatus for forcing the gases through the limestone.